In recent years, in order to improve performance of various safety devices, for example, of a seat belt and an airbag provided at a vehicle, operations of such safety devices may be controlled in accordance with a weight of an occupant seated on a seat of the vehicle. For example, in a case where the occupant seated on the seat does not tighten and fasten the seat belt, a warning lamp is generally turned on for indicating that the seat belt is not fastened after the detection that the occupant is seated on the seat. In addition, according to regulations in the North America, an air bag is required to be deployed at a vehicle crash in a state where an adult is seated on a passenger seat. In a case where a child seat is installed on the passenger seat to face the back of the vehicle so that an infant or a child faces a driver of the vehicle, the air bag is required not to be deployed. Therefore, correctly and appropriately determining the weight of the occupant is extremely important for a safety aspect.
JP09-207638A discloses an occupancy detection apparatus for determining whether or not an occupant is seated on a vehicle seat by detecting a load applied to the seat. According to the occupancy detection apparatus disclosed in JP09-207638A, two load sensors are arranged at two seat attachment portions among four seat attachment portions at which the seat is fixed to a vehicle floor. Specifically, one of the load sensors is provided at the seat attachment portion at a front side of the vehicle while the other of the load sensors is provided at the seat attachment portion at a rear side of the vehicle. Whether or not the occupant is seated on the seat is determined on a basis of a sum of two load values obtained from the two load sensors.
According to the occupancy detection apparatus disclosed in JP09-207638A, the load sensors may be provided at the left front and rear attachment portions or the right front and rear attachment portions, for example, so as to minimize the number of load sensors for determining whether or not the occupant is seated on the seat while reducing cost and weight of the apparatus.
Nevertheless, in a case where the load sensors are provided at the left front and rear attachment portions or the right front and rear attachment portions, the sum of the load values detected by the load sensors may fluctuate when the vehicle is driven around a corner, i.e., the vehicle is turning, which may result in a wrong determination of whether or not the occupant is seated on the seat. For example, in a case where two load sensors are provided at a front end and a rear end of an inner portion of a passenger seat in a width direction of the seat of a left-hand drive car, the sum of the load values detected by the load sensors may decrease due to a centrifugal force applied to the seat of the vehicle while the vehicle is turning left. Therefore, even when the adult is seated on the passenger seat, it is wrongly determined that no occupant is seated on the passenger seat.
A need thus exists for a seat occupancy determination apparatus which is not susceptible to the drawback mentioned above.